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Unit of temperature with the base as a minimum temperature a matter can be. 0 k (zero Kelvin) is -273 degrees Celsius. (developed by William Thomson). More practically speaking, the Kelvin temperature scale measures an object's temperature above absolute zero, the theoretical coldest possible temperature. On the Kelvin scale the freezing point of water is 273 ( = 0o C = 32o F) [ K = 273 + C = 273 + 5/9 * (F-32)]. The Kelvin temperature scale is often used in sciences such as astronomy.
Johannes Kepler was the first to model planetary orbits as ellipses instead of circles. With Tycho Brahe's observations of planetary motion in the sky, Kepler had the data he needed to test his "crazy" idea. In 1609, he published the fruits of his effort in a book called "Astronomia nova" or "The New Astronomy" where he summarized planetary motion with three rules, or laws.
Law of Ellipses (Kepler's First Law) A planetary orbit is an ellipse with the Sun at one focus. The other focus lies on the opposite end along the ellipse's major axis, close to where the planet reaches aphelion.
Law of Equal Areas (Kepler's Second Law) As a planet orbits the Sun, the planet divides the ellipse into equal areas in equal time with a line drawn between the planet and the Sun. This behavior means that the planet's orbital velocity varies with distance from the Sun: at perihelion, the planet is at maximum speed and at aphelion the planet crawls along at minimum speed.
Harmonic Law (Kepler's Third Law) Even though the orbital velocity of a planet changes constantly, one relationship does remain constant. The orbital period is directly related to the average distance between the planet and the Sun. This law implies that planetary orbital velocity decreases with increasing distance from the Sun. For instance, the orbital velocity of Mercury (47.9 km/s) is far greater than Pluto (4.7 km/s).
1 kg = 1000 grams = 2.2 pounds, the mass of a liter of water.
1km = 1000 meters = 0.62 miles.
Kinematics
Kirchhoff's
Law of Radiation
Kirchhoff's Laws Kirchhoff's
First Law
Kirchhoff's
Second Law
Kirchhoff's
Third Law
Kuiper
Belt
L0
Landslide.
Intersecting valley complex.
Lagrange showed that three bodies can lie at the apexes of an equilateral triangle which rotates in its plane. If one of the bodies is sufficiently massive compared with the other two, then the triangular configuration is apparently stable. Bodies at such points are sometimes referred to as Trojans. The leading apex of the triangle is known as the leading Lagrange point; the trailing apex is the trailing Lagrange point. Collinear with the two large bodies are unstable equilibrium points which can sometimes be useful places for spacecraft, i.e. SOHO.
Laser
The closest an object can circle a black hole without being pulled in.
The angular distance of a celestial body from the ecliptic. Celestial latitude may be geocentric or heliocentric; heliocentric is sometimes referred to as true latitude.
Molten rock released from the interior of a planet.
Law of Areas
Law of Electric Charge Preservation The electric charges held by matter doesn't increase or decrease if no exchange of electric charge with outside takes place. This law is called Law of Electric Charge Preservation.
Leap Year
Any of three types of negatively charged subatomic particles created in the Big Bang, only the electron still exists.
A wobble in the Moon's rotation that allows observers to see slightly more than half of its surface.
An instrument similar to radar that operates at visible wavelengths.
Light
Brightness or intensity of light plotted against time on a graph. Astronomers discover dark stellar companions using the light curve of the star. As a dark orbiting object eclipses the star, the brightness falls, producing a dip on the light curve. Careful analysis of the light curve reveals the masses of the star and dark companion plus the distance to this eclipsing binary system.
A measure of a telescope's ability to collect light. Light gathering power is proportional to the telescope's lens or mirror surface area. Astronomers enjoy observing through large aperture telescopes because they may see faint, distant objects and detail of nearby objects.
A glow in the sky, caused by streetlights and atmospheric pollution, that blocks astronomers' view of faint objects.
One light year is the length of how much light can travel in a year. 1 light year = 9.46053*1012 km (= 5,880,000,000,000 miles = 63,239 AU).
The outer edge of the apparent disk of a celestial body.
Elongate marking.
Line
Broadening
Line Profile
l liter = 1000 cm3 = 1.06 US quarts.
Also Orion Arm. The spiral arm of the Milky Way Galaxy in which the Sun lies.
Our galactic neighborhood, including the Milky Way, Andromeda Galaxy, M33, and more than 25 smaller galaxies. The Local Group appears to be a suburb of a supercluster of galaxies that lies 60 million light years away, in the direction of the constellation Virgo (Virgo Supercluster).
Local
Standard of Rest
Local Supercluster
Angular distance measured along a great circle of reference, from the intersection of the reference circle with an adopted zero meridian to the similar intersection with the meridian passing through the object whose position is being defined. Celestial longitude is measured eastward along the ecliptic from the vernal equinox to the great circle passing through the pole of the ecliptic and the object. It may be geocentric or heliocentric.
An orbit about 200km above Earth's surface. Low-Earth orbits are used by the space shuttle, space stations, and many satellites.
A measure of the rate of energy flowing from a source, like a galaxy, star, or light bulb. Luminosity tells astronomers how fast energy "leaks" from the star. Luminosity is a measure of power divided into units called watts. Given the luminosity of a star, an astronomer can calculate the distance to the star by measuring the star's brightness. Temperature and luminosity are related, but dependent on the mass and size of a star.
A shorthand description of a star based on spectral line widths. Our Sun is a G2 V star. The Roman numeral V denotes the luminosity class, which is the main sequence, while G2 refers to a spectral class. Luminosity class numerals range from I to V. For a given spectral type, the luminosity of the star increases from V on up to I. Thus, a B8 I supergiant star luminosity is far greater than a B8 V main sequence star; yet the surface temperatures are equal. The prominent hydrogen absorption-line patterns are the same for both stars; but, the width of the absorption lines differ. The B8 V star lines are wider than the B8 I lines, indicating a vast difference in luminosity.
The average time between successive new or full moons, equal to 29 days 12 hours 44 minutes.
Lunar Eclipse
The Moon passes through its phases every 29.5 days. The same phase will fall on the same date of the year according to the Saros cycle, every 18 years, 11 days, and eight hours.
In conjunction with the Sun; rises and sets with it. 0 percent illuminated, 0 degrees elongation.
Prominent just after new moon at sunset; less than 50 percent illumination.
In opposition with the Sun; rises at noon and sets at midnight; 50 percent illuminated, 90 degrees east elongation.
Lunar illumination increasing between first quarter and full.
Rises at sunset and sets at sunrise; 100 percent illuminated, 180 degrees elongation.
Decreasing illumination decreasing between full and last quarter.
Rises at midnight and sets at noon; 50 percent illuminated, 90 degrees west elongation.
The interval between one new moon and the next: that is, 29 days, 12 hours, and 44 minutes.
Lyman
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